This invention relates to plasma-enhanced chemical vapor deposition reactors and in particular to a method of improving the performance of such reactors following an in-situ clean of the reaction chamber.
Plasma-enhanced chemical vapor deposition reactors are widely used in the semiconductor industry to deposit thin films onto semiconductor wafers. As a byproduct of the deposition process, a thin film is also deposited on the walls of the reactor chamber, and this film must be periodically removed. Otherwise, the material on the walls of the reaction chamber will begin to flake off during the deposition process and land on the wafer, seriously reducing the yield of acceptable chips from the wafer.
One method of cleaning the walls of the reactor chamber is an in situ process. This type of process uses a plasma generated in the chamber to remove the thin film from the walls. In situ processes are generally quicker to perform and result in less down-time than cleaning processes that require the reactor to be disassembled.
One in situ cleaning process, for example, uses a plasma of NF3 and O2. HF is a byproduct of the cleaning plasma. Following the cleaning process, it has been found necessary to xe2x80x9cpassivatexe2x80x9d the reaction chamber to eliminate some of the effects of the plasma before resuming the normal processing of wafers. In particular, during the cleaning the walls of the chamber tend to become impregnated with F or HF, and these materials xe2x80x9coutgasxe2x80x9d (i.e., are expelled from the walls) during the subsequent deposition process. The outgassing molecules enter the thin film that, as described above, forms on the walls during processing and loosen the film, creating flaking. The outgassing molecules may also impregnate the thin film that is being deposited on the wafer, creating adhesion problems.
When films of a relatively low percentage (e.g., xe2x89xa65%) of a dopant (e.g., phosphorus) are being deposited, flaking has been prevented by using a capacitively-coupled hydogen plasma (CCP) to passivate the chamber after cleaning. With films of a high percentage of dopant, however, this passivation process has been found inadequate, even when extended for periods substantially longer than the normal passivation.
Hence there is a need for a passivation process that can prevent flaking from the walls of the chamber because of outgassing after a deposition of a highly-doped film.
In accordance with this invention, an inductively-coupled hydrogen plasma (ICP) is used to passivate the reaction chamber after in situ clean. Use of an ICP has been found to materially reduce the flaking of material from the walls of the chamber during a deposition of a highly-doped thin film.